# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Gyro sextant
From: Sean C
Date: 2019 Jan 24, 23:02 -0800

Bill,

"As the gyro rotor spins, any deviation from the vertical will cause the spindle (the axis of the rotor) to precess. This is because the force of gravity pulling one side of the rotor down, due to the offset center of gravity, combines with the velocity of the spinning rotor producing a downward force 90° ahead of the lowest point of the rotor in the direction of the rotation. The rotor will then move to lean in that direction, which again causes the downward force to move 90° ahead of that direction. This process will continue, causing the axis of the rotor to describe a cone in space. If the velocity of the rotor is high enough, the rounded end of the spindle acting like a wheel will apply an accelerating force to the precession. In the same way that the downward force of gavity causes precession, the acceleration of precession causes a force opposing gravity - lifting the rotor and aligning it with the axis around which it precesses: the vertical. At the same time, the precessional velocity decreases and the rotor stabilizes in the exact same way that can be seen in a child's spinning top. It should be noted, however, that this phenomeneon only occurs when the gyro is supported below its center of gravity. Gyros that are supported above their center of gravity will precess in a direction opposite to the spin of the rotor. Therefore, the spinning wheel action of the spindle will work to slow the rate of precession which will cause a force in the same direction as that of gravity - causing the axis of the rotor to be pulled away from the vertical. Precessional velocity will then increase and the gyro will become increasingly unstable."

Regards,

Sean C.

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